In the field of this invention it is known that many communications systems employ common channels. These channels are used to send information from a single transmitting point to specific desired receiving points. In general, when using common channels, all receiving points are “listening” for a transmission that is intended for them. A specific receiver to which a given transmission is sent is normally identified via an “address” or ID field within the common transmission. Each receiver uses this address to identify whether or not the transmission was intended for it. If not, the transmission is discarded. If the address field matches that of a given receiver, the receiver will attempt to fully decode the sent information.
An example of such a common channel implementation is the HS-SCCH (High-Speed Shared Control Channel) as specified by 3GPP (3rd Generation Partnership Project) release 5.
A problem exists within the current release 5 specifications for 3GPP TDD (Time Division Duplex) mode, whereby a Transmit Power Control (TPC) based power control scheme is used to control the transmit power of the HS-SCCH. User equipment (UE) is capable of measuring the signal to interference ratio SIR of HS-SCCHs that were correctly decoded by the UE (and hence intended for that UE). The UE then compares the measured SIR with a nominal target SIR and generates binary TPC commands that indicate to the transmitter whether the power should be increased or decreased. The nominal SIR target is set based upon the target error rate. For low target error rates, a high SIR target will be set, and vice versa. Also, the SIR target required to attain a target error rate will vary with the radio channel propagation conditions. Parameters that affect this “SIR-to-error-rate” mapping are, for example, UE speed and the amount of multipath (reflections) in the channel. It is therefore the job of the UE (in the TPC-based power control scheme) to autonomously adapt the SIR target in response to a measured error rate, or error statistics. Without correct error statistics, the UE is unaware of how well it is doing in controlling transmit power and the target error rate may not necessarily be met.
However, this approach has the disadvantage(s) that in the TPC scheme for the HS-SCCH common channel the UE is unable to distinguish between a transmission not intended for it (the decode will fail) and a transmission that was intended for it but was corrupted by noise and/or interference. This inability to detect how many messages were actually transmitted to the UE is a problem since the UE is therefore unable to determine the actual error rate (the UE knows how many overall messages were in error, across all UEs, but does not know how many were sent to it, nor how many of those sent to it were in error). As such, the TPC based power control scheme for the HS-SCCH common channel cannot be made to operate correctly, or at least it will be very difficult for the UE to reach the correct error rate.
A need therefore exists for system, transmitter, receiver and method for communication power control wherein the abovementioned disadvantage(s) may be alleviated.